1. Field of the Invention
The present invention relates to a method of repairing a bump or divot defect of a structure and, more particularly, to a method of repairing a defect of a structure, suitable for repairing a defect of a phase-shifting mask.
2. Description of the Related Art
In recent years, a phase shift mask in which a resolution is improved using a phase shift effect is used as a mask for transferring an LSI pattern to a wafer. In such a phase shift mask, when a defect occurs in a shifter, preferable pattern transfer cannot be performed. For this reason, when the defect occurs, the defect must be reliably repaired.
The following method is proposed. That is, when a bump defect is present in the shifter of a phase shift mask, and a focused ion beam is irradiated on the defect, the defect is repaired by etching the bump defect. However, since the phase shifter and a mask substrate often consist of the same material, this method cannot easily detect the end of etching of the bump defect. In addition, even if only the bump defect can be etched, the shape of the shifter after etching depends on the shape of the projecting defect.
In order to solve the above problem, the following method can be considered. That is, the projecting defect is covered with a deposition film so as to flatten the upper surface of the film, the deposition film including the bump defect is etched by a focused ion beam under a condition in which the projecting defect and deposition film are etched at the same rate, thereby removing the bump defect together with the deposition film.
In assisted deposition using the focused ion beam, however, it is difficult to deposit some types of films on the bump defect so as to flatten the upper surface of the film. When the thickness of the deposition film is increased to some extent, the size of a deposition film step at a portion where the edge of the bump defect is covered with the deposition film is decreased. However, even when a film having a thickness larger than that of a predetermined thickness is deposited, the deposition film step is not easily flattened. When the film having the step is etched, the shape of the etched structure depends on the shape of the step, and the mask surface can not be flat after removing the bump defect.
In repairing a divot defect, it is very difficult to repair the defect such that the surface of a buried portion is set on the same plane as that of the remaining shifter surface.
As described above, it is conventionally considered that the defect of a phase shift mask is repaired using a focused ion beam. Since a deposition film cannot be easily formed on the defect so as to obtain a flat surface, the defect cannot be easily repaired to be flattened at the same level as that of the substrate surface.